全文获取类型
收费全文 | 743篇 |
免费 | 105篇 |
国内免费 | 111篇 |
专业分类
化学 | 406篇 |
晶体学 | 18篇 |
力学 | 31篇 |
综合类 | 5篇 |
数学 | 13篇 |
物理学 | 215篇 |
综合类 | 271篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 25篇 |
2017年 | 29篇 |
2016年 | 56篇 |
2015年 | 36篇 |
2014年 | 50篇 |
2013年 | 71篇 |
2012年 | 37篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 48篇 |
2008年 | 36篇 |
2007年 | 50篇 |
2006年 | 43篇 |
2005年 | 38篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
排序方式: 共有959条查询结果,搜索用时 187 毫秒
861.
Yuming Shang Hao Jin Jianwei Guo Shaoguang Feng Jingming Xu 《European Polymer Journal》2006,42(11):2987-2993
To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfonated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by 1H NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4′-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfonated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 × 10−3 to 7.2 × 10−2 S cm−1 and low methanol permeability of less than 2.85 × 10−7 cm2 s−1. Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure. 相似文献
862.
本文报道以均匀共沉淀法制得 Sbx Sn1 -x O2 体系半导体气敏材料 ,研究了固溶体组成与电导的变化规律 ,并对导电机制进行了讨论。结果表明 :x<0 .30时均可生成固溶体。微量 Sb(x=0 .0 4 )的掺入即能提高 Sn O2 电导一个数量级 ,在 x≤ 0 .0 4区间电导都呈上升趋势 ,其后一直到固溶范围内随着 X增加 ,电导反而缓慢下降。根据体系中存在的 Sb°Sn和 Sb′Sn两种缺陷 ,讨论了其电导变化和导电机制。认为平衡 Sb°Sn 2 e′=Sb′Sn对上述导电机制起决定作用。XPS分析对 Sb5 、Sb3 的含量进行了确认 ,交流阻抗谱的测试结果从另一角度对电导行为加以证实。 相似文献
863.
导电炭黑在聚丙烯/极性聚合物体系中的选择性分散及其对导电性能的影响 总被引:4,自引:0,他引:4
以聚丙烯(PP)和极性聚合物的共混物为基体材料,以导电炭黑为填料,通过熔融共混制备导电复合材料。探讨了导电炭黑在两相基体中的分散情况以及双基体各组分比例对复合体系结构形态和导电性能的影响。SEM测试结果表明:炭黑粒子选择性地分散在极性乙烯-丙烯酸共聚物(EAA)树脂或尼龙6(PA6)中。EAA相在PP基体中呈棒状伸长结构,且随着EAA树脂含量的增大,在PP基体中形成更多更为连续的棒状伸长结构,使体积电阻率迅速下降。当在体系中加入PA6,mPP/mPA6=80/20时,PA6在PP基体中形成相互连接的纤维状分散结构,显著降低了复合体系的体积电阻率。电性能测试结果表明:材料在相同导电炭黑含量下的体积电阻率相对单基体体系可降低3~7个数量级。 相似文献
864.
865.
The electrical conductive molecular crystals (Me3NEt)[Pd(dmit)2]2 and (NEt4)[Pd (dmit)2]2 (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been prepared, and their crystal structures and conductivity-temperature curves have been determined. The fact that the conductivity at room temperature of (Me3NEt)[Pd(dmit)2]2 (a = 58 Ω· cm-1) is much higher than that of (NEt4)-[Pd(dmit)2]2(cr= 2.2 Q~1 ?cm'1) has been rationally explained by the results of energy band calculations. (MeNEt3)[Pd(dmit)2]2 belongs to monoclinic system, P21/m space group and (NEt4)[Pd (dmit)2]2 belongs to triclinic system, P1 space group. The structural conducting component of the crystals is the planar coordinative anion [Pd(dmit)2]05- which forms the face-to-face dimmer [Pd(dmit)2]2-. These dimers have been further constructed to be a kind of two-dimensional (2-D)conductive molecular sheet by means of S…S intermolecular interactions. The tiny difference of the above 2-D molecular sheets of the two title crystals has resulted in one 相似文献
866.
This study demonstrates that single‐chain π‐conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne‐type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π‐conjugated systems, which partially cancel each other out. It is probable that we can design one‐dimensional polymers with HOMO–LUMO gaps small enough to be conductive by combining the above‐mentioned oligomers with each other as monomer units in the polymer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
867.
复合型炭系导电发热涂料的研究 总被引:6,自引:0,他引:6
采用复合型炭系填料石墨、炭黑、煅烧石油焦、石墨纤维、炭纤维和碳化硅粉末等与合成改性树脂经机械混合及不等温固化,制得并联导电发热涂料;利用扫描电镜、伏安法体积电阻率测试仪和电参数测定仪对涂层进行测试分析.研究结果表明:在安全电压下,该涂料具有加热迅速、使用安全、热效率高等特点,而且热传导和热辐射性能优良;在填料含量相同时,复合型炭系填料优化配方后所制得的涂层比单一填料具有更优良的导电特性;炭系填料与纤维匹配后构成了三维空间网络导电粒子链结构,更利于导电和发热;在60 V电压下,通电14 min,自制电热壁画涂层表面温度达到134.8 ℃;树脂基体改性后电发热涂料的附着力提高,耐温变性和耐热性等能力增强. 相似文献
868.
通过对不导磁材料高精度凸缘轴承套圈的加工工艺进行探讨,在轴承套圈磨加工时,采用了导磁附件,二级工装,粘导磁片的方法,使无磁钢凸缘微型轴承套圈的加工转化为常规轴承套圈的加工。 相似文献
869.
导电沥青混凝土作为一种新型材料,具有广泛的应用前景.目前国内外对导电沥青混凝土的研究主要侧重于融雪化冰的电热性能研究[-6],而对于其导电机理的研究却相对甚少,且不够深入.导电沥青混凝土的导电机理相当复杂,到目前为止,还没有一个导电模型能够很好的解释导电沥青混凝土的导电行为.本文在前人研究的基础上,借鉴聚合物基导电复合材料的导电机理,对导电沥青混凝土的导电机制进行数值模拟,提出较为完善的导电沥青混凝土导电机制. 相似文献
870.
Chia‐Lung Lin Wen‐Yen Chiu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1648-1659
The electrically conductive polypyrrole/dodecylbenzene sulfonic acid/poly(N‐isopropylacrylamide‐co‐acrylic acid) (PPy/DBSA/poly(NIPAAm‐co‐AA)) composite microgels were synthesized by a chemical oxidation of pyrrole in the presence of DBSA as the primary dopant, and poly(NIPAAm‐co‐AA) microgels as the polymeric codopant and template, in which APS was used as the oxidant. It was proposed to prepare “intelligent” polymer microgel particles containing both thermosensitive and electrically conducting properties. The polymerization of pyrrole took place directly inside the microgel networks, leading to formation of composite microgels and the morphology was observed by transmission electron microscope. PPy particles interacted strongly with microgels, as the acid groups of microgels acted as the polymeric codopant. The composite microgels thus formed showed electrically conducting behavior dependent on humidity and temperature. At temperatures lower than lower critical solution temperature, the conductivity decreased with increasing the humidity and a small hysteresis phenomenon was observed. The hysteresis became indistinct when temperature was near volume phase transition temperature. However, after the treatment of high temperature and high humidity, the conductivity increased surprisingly due to the structure reorganization inside the composite microgels. The distinctive functionality of the PPy composite microgels was expected to be utilized in many attractive applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1648–1659, 2006 相似文献